The importance of zinc in living systems has long been recognized. Zinc ions serve multiple biological functions that may be classified as catalytic, structural, or regulatory. The catalytic activity of zinc is due to its Lewis acidity, which serves to activate reactants as in well-described enzymatic mechanisms such as that of carboxypeptidase. Zinc plays a structural role in supporting higher order protein structure by coordinate interactions with cysteine or histidine residues, and examples such as those found in “zinc finger” type transcription factors are also well-known. However, the regulatory function of zinc, which relates to the effect of “free” zinc (defined here as loosely- and non-protein bound zinc) on processes such as cellular metabolism and transcription, remains a complex subject of considerable recent interest and discovery. For example, under oxidative stress conditions, cellular zinc release results in a multitude of pathologies on the organismal level.
Zinc ionophores are capable of transporting zinc ions (hereinafter, simply referred to as zinc) between the extracellular environment and the intracellular environment. One example of a zinc ionophore is ZnHPT, 1-hydroxypyridine-2-thione, also known as pyrithione. ZnHPT has poor aqueous solubility.